diff -u b/core/lib/Drupal/Core/Theme/ThemeInitialization.php b/core/lib/Drupal/Core/Theme/ThemeInitialization.php --- b/core/lib/Drupal/Core/Theme/ThemeInitialization.php +++ b/core/lib/Drupal/Core/Theme/ThemeInitialization.php @@ -248,9 +248,9 @@ $token = substr($token_candidate, 1); // Prime extensions. - $this->getExtensions(); - if (isset($this->extensions[$token])) { - return str_replace($token_candidate, $this->extensions[$token]->getPath(), $css_file); + $extensions = $this->getExtensions(); + if (isset($extensions[$token])) { + return str_replace($token_candidate, $extensions[$token]->getPath(), $css_file); } } }